Shielded filament assembly for orbiting electron type vacuum pump



1967 c. B. SIBLEY SHIELDED FILAMENT ASSEMBLY FOR ORBITING ELECTRON TYPE VACUUM PUMP Filed Feb 15, 1965 United States Patent 3,353,055 SHIELDED FILAMENT ASSEMBLY FOR ORBIT- ING ELECTRON TYPE VACUUM PUMP Clifton B. Sibley, Needham, Mass., assignor to National Research Corporation, Cambridge, Mass, at corporation of Massachusetts Filed Feb. 15, 1965, Ser. N0. 432,749 1 Claim. (Cl. 313-276) ABSTRACT OF THE DISCLOSURE An orbiting electron vacuum pump with a filament assembly, reflector shield and grid supported from lead wires via an insulating header. The filaments are helical and the arrangement accommodates these without disrupting the necessary electric field for the orbiting electron operation.

The present invention relates to orbiting electron devices and particularly to vacuum pumps of the orbiting electron type (orbitron pumps).

It is the principal object of the present invention to provide an improved orbitron pump with increased ease of operation, operating life and reliability compared to prior art pumps.

The invention features an improved arrangement of the pump electrode and filament supports which allows a wide tolerance in the pump anode orientation. Also, there is provided a plug-in filament assembly so that filaments can be replaced easily by the user.

Other objects, features and advantages of the invention will in part be obvious and will in part be described hereinafter.

The invention is now described in terms of a preferred embodiment and with reference to the accompanying drawings wherein:

FIG. 1 is a sectional view of the closed end of an orbitron pump;

FIG. 2 is an exploded isometric view of portions of the same pump; and

FIG. 3 is a cross-sectional its electrical power supply.

Referring now to FIG. 1, there is shown an annular orbitron pump body with a necked down opening 12. The opening is sealed by a cover plate 14. Contained within the pump body and supported from the cover plate are an anode rod 16, mounting one or more slugs of getter material 18, a plug-in filament assembly 20, a grid 30 and a shield 40.

The plug-in filament assembly, shown in FIG. 2, comprises a glass header disc 21 with a central aperture 22 and eight sealed-in lead wires: 31, 41, 23, 25, 32, 42. 26, 24. The lead wires are diameter and made of nickel. Pairs 23, 25 and 24, 26 of the wires are bent as shown in FIG. 2 to provide conductive supports for first and second pump filaments 27 and 28, respectively. The filaments are .009 inch diameter tungsten or tungsten-26 rheniurn alloy bent into coils (7 /2 turns, coil diameter .029 inch and coil length about inch), the ends of which are spot welded to the supports. Wires 31 and 32 mount the grid 30 and wires 41 and 42 mount the shield 40.

FIG. 2 also shows the shield 40 and the anode 16. Grooves 43 and 44 are cut in the shield to accommodate wires 24 and 26, respectively. The wires pass through these grooves without touching the shield. The shield view of the pump showing 3,353,055 Patented Nov. 14, 1967 is a stainless steel spinning with a central aperture 43 having an inner diameter of 6 inch.

Referring again to FIG. 1, the assembly of the parts can now be described. The assembly 20 is plugged in to clips mounted on wire leads 52 sealed into the cover plate 14. The anode is mounted along the center line of the pump body and passes through the apertures 22 and 43. The shield 40 is mounted on the leads 41 and 42 high enough to define the end or" the pump electrical field clear of the necked down opening 12. The grid 30 consists of a series of circular wires spot welded to two tie wires. one of which is indicated at 33. The tie wires are welded to the leads 31, 32.

The wires 24, 25 are bent so that they shadow the filaments 28, 27 from the anode 16.

Electrical connections for the pump are shown in FIG. 3. The pump electric field is established between the anode 16 and the grounded pump body 10 by a 10 kilovolt DC. power supply. The filaments are biased positively with respect to ground (about 300 volts), and powered by transformers 21. Electrons emitted from the filaments spiral about the anode 16 until they collide with a gas molecule or with the anode 16 or slug 18. The collisions with gas molecules produce positive ions which are attracted to the wall 10 and there pumped by titanium deposited on the wall by titanium from slug 18. The pumping mechanisms comprise chemical combination, physical adhesion and burial. The grid 30 is biased at about 1000 volts to accelerate the ions toward the wall and confine the effective electric field of the pump.

The advantages of the present invention are that it provides a plug-in assembly which is disposable after filament burn-out. The grid 30 and shield 40 may be salvaged, if desired, in changing filament assemblies. The principal feature of the plug-in assembly is a conventional header disc, such as the octal glass disc used in the preferred embodiment, with at least one pair of sealed-in lead wires (e.g. wires 23, 25) located in different radial (with respect to the anode) planes, the wires being bent to cross a common radial plane with a filament (27) secured between the wires in said plane, one of the wires (25) being bent so that it shadows the filament from the anode.

The vertical center line of the filament coil in my pre ferred embodiment is inch away from the center of the inner supporting lead wire while the lead wire is spaced about /2 inch from the center anode. The ends of the helical filament are supported from the lead wires and the filament wire extends radially inwardly towards the inner lead wire to support the helical portion of the filament next to the inner lead wire.

I have found that such an arrangement does not disturb the pump electric field as much as prior art filament arrangements and that my arrangement allows the use of a helical filament. A helical filament is much more resistant to heat shock than a straight filament, and provides more effective surface than a wire or ribbon filament for electron emission and heat dissipation.

The helical filament tends to emit its electrons directly to the anode and cannot provide an orbiting electron cloud unless the above dimensional relations are observed. Expressed as ratios, the above dimensional relations can be characterized by the degree of masking of the helical filament by the inner lead wire support. The inner lead wire should physically mask between /2 and A the coil diameter of the helical filament from the anode and the lead wire should be sufficiently close to the filament (2 lead wire diameters or less) that the small bias on the lead wire can supplement its physical masking effects.

3 4 The plug-in header of my invention can be divided into provide a low positive bias thereto, current supply severalparts, such as pie-shape wedges, so that filaments means for heating the filament so thatelectrons are can be replaced individually. There can be only one filaemitted from the filament and constrained to orbit ment in the pump or as many as four or five. around the anode several times before colliding with What is claimed is: 5 the anode. An improved orbiting electron device comprising, in (e) the support of said filament assembly being a seccombination: 0nd pair of Wires sealed into the closure plate and (a) an annular vacuum-tight metal wall with a closure ending in terminal means, the said first pair of lead plate at one end of said wall, an anode electrode and wires being held by said terminals and the said first a filament assembly supported from said closure pair of lead wires being sealed into said header disc, plate; the header disc being constructed with a central open- (b) the said anode electrode comprising a rod extending to allow clearance of the anode electrode, and

ing along the center of the annular space defined by (-f) a metal end shield surrounds the anode with a porthe wall; tion of the shield extending radially outwardly from (c) the filament assembly comprising a helical filament the anode without touching the anode, the longituwith the helix axis parallel to and offset from the dinal location of said shield portion being between the anode rod electrode, the filament assembly further header disc and the filament helical portion, and comprising a header disc of insulating material with wherein said voltage supply means are connected to lead wires sealed therein, two of said lead wires being said end shield to provide a grounding bias thereto adjacent to and circumferentially straddling said filaand wherein the end shield is supported from the merit, a first one of said Wires being bent to cross headef disg between said filament and anode and extending parallel to said anode and filament helix axis and being References Cited connected to the filament at one end to support said UNITED STATES PATENTS filament, the other of said leads extending to the other end of said filament to further support said 13061912 6/1919 Keyes 313-275 filament; the said first lead wire partially masking 1/1928 Zworykm 313' 275 the helical filament from the anode and being located 2422142 6/1947 Skehan 313272 61056 to the filament; and 3,244,969 4/1966 Herb et a1 313fl7 x (d) electrical voltage supply means connected to said 3,274,326 9/1966 Moms et a1 313-7 X annular wall to provide a ground bias thereto and connected to said anode to provide a high positive DAVID GALVIN Primary Exammer' bias thereto and connected to said filament leads to 

